Internal combustion engines use motor oil to lubricate their moving parts. The oil is collected in an oil pan when the engine is not in operation. In order to replace the oil in the engine after it has been used for some time, and has become contaminated with dirt and particulate matter, a means to drain the oil pan must be available. This means of draining is universally provided by means of a threaded drain hole on the underside of the oil pan. The drain hole is sealed with an oil pan bolt during operation of the engine.
In order to change the oil in an engine, the used oil must be drained from the engine. This is accomplished by removing the oil pan bolt from the drain hole, and allowing the oil to drain out into a receptacle. Traditionally, this has involved the oil changer getting his hand covered with hot oil.
Oil drains best when it is heated and therefore less viscous. Oil is therefore usually changed after the engine has been operated so that the oil is heated. Most vehicle engines hold at least a gallon of oil, so the pressure on a drain hole is considerable. As the oil pan bolt is removed, the threads of the plug leave the threads of the drain hole. Once the bolt is out of the hole, hot oil gushes out of the oil pan, usually covering the operator's hand.
This very often results in the oil pan bolt being knocked out of the operator's hand and into the receptacle for the used oil. Thus in addition to the initial hot oil bathing, the operator is provided the opportunity to retrieve the oil pan bolt from the bottom of the used oil receptacle.
In addition to it being nearly impossible to change oil without getting a handful of hot oil with the current art oil pan bolt, it is also extremely easy to misplace the plug during an oil change. Once the bolt is removed, it must be said aside while the oil drains. It is therefore quite common for an operator to kick the plug somewhere where it cannot be found. This necessitates a trip, in another vehicle, to an auto parts store to obtain another oil pan bolt to finish the oil change.